I thought it might be worth starting up a topic focussing on who we personally consider to be the 5 greatest Mahayana masters of all time, and a few sentences on what makes them so significant.

1. Shakyamuni Buddha...our original teacher
2. Garab Dorje....the 1st Dzogchen Atiyoga teacher
3. Padmasambhava....the 2nd Buddha
4. Rongzom Dharmabhadra...the lion of philosophy and 1st great omniscient Vajradhara king of all Buddhas!
5. Longchen Rabjampa...the 2nd great omniscient Vajradhara overlord of all the Buddhas!
6. Jamgon Mipham....hero of Great Madhyamaka and the 3rd great omniscient Vajradhara king of all Buddhas!

Because the nature of beings is to be affected by different things, and fortunately, because the nature of Compassion is to be as infinite as we are,
I can list the 5 historical masters who I believe have had the most impact, on human beings at least, in disseminating true understanding of the Dharma...

(The list given by "Buddhanataka" almost directly correlates to mine. The order that they directly affect me in this current age is only slightly different):

1. Garab Dorje - First human Dzogchen master -because of his direct teaching, pointing out the point to us- without whom I would constantly forget the simplicity
2. Padmasambhava - without whom the Vajrayana wouldn't have reached Tibet and may have disappeared altogether- without whom all future generations wouldn't have been inspired to keep the lineage unbroken to this very day, through our current teachers to us, and without whom I wouldn't have any transmission
3. Shakyamuni Buddha - the great human example, the foundation of all Dharma, whether we had the capacity to hear or not -without whom I wouldn't have the inspiration for perseverance, courage and omniscience
4. Longchen Rabjampa - the great ellaborate explainer of details - who shows me the vastness and completeness of the Dharma
5. Rongzompa - the unequalled holder and expounder of the View of the essence of Dharma -without whose clarity and specificity I would have nothing to compare my own view with

The 5 Masters from the Golden Age that still have the most impact on today's practitioners are:

1. Milarepa - the ultimate hope for all those that think they are too corrupt to be Enlightened in one lifetime
2. Jamyang Khyentse Wangpo the Great - for the vastness of his knowledge and integrated wisdom
3. Jamgon Mipham - for his unobstructed clarity and passing down of skills
4. Jigme Lingpa - for embodying unconditional devotion
5. Patrul Rinpoche - for his transparency and unaffected frankness

And the 5 Masters that today have the most direct impact on my life and my path:

1. H.H.14th Dalai Lama - who, like for most people, was my earliest inspiration and reason to come to the Dharma
2. Sogyal Rinpoche - whose devotion for his teachers, warmth and teachings on integration affect my daily life
3. Namkhai Norbu Rinpoche - whose vastness of knowledge and direct teaching of the essence is unexcelled
4. Dzongsar Khyenste Rinpoche - whose precision, creativity and non-conformity make me feel at home and free
5. Dzigar Kontrul Rinpoche - whose sharp, clear explanations and their integrity in his life are an example to all

1Myriad dharmas are only mind.
Mind is unobtainable.
What is there to seek?2If the Buddha-Nature is seen,
there will be no seeing of a nature in any thing.3Neither cultivation nor seated meditation —
this is the pure Chan of Tathagata.4With sudden enlightenment to Tathagata Chan,
the six paramitas and myriad means
are complete within that essence.

"Even if you practice only for an hour a day with faith and inspiration, good qualities will steadily increase. Regular practice makes it easy to transform your mind. From seeing only relative truth, you will eventually reach a profound certainty in the meaning of absolute truth."
Kyabje Dilgo Khyentse Rinpoche.

Bodhipaksa is a Buddhist writer and teacher, originally from Scotland I think (or was it Ireland?) but currently in the States. His site is http://www.wildmind.org/" onclick="window.open(this.href);return false; and has been of great help to many. He is modern, eclectic, and exemplary in his kindness. I think he has a bit of the Dalai Lama in him.

Kye ma!
The river of continuity is marked by impermanence.
Ceaseless flowing of appearance.
Beautiful and repulsive.
The dance of life and death is a display of the vast expanse.
With gratitude the watcher and the watched pass through the barrier of duality.